Patent EA-002876-B1 (EA)
Title: Shaping method for producing plastic parts and device for carrying out said method
IPC: B29C45/02
Filed: 1999-10-27
Abstract: 1. Molding process for the production of plastic parts in which the molten molding material is fed, before molding in a mold cavity (KV), into a repository space (A), implemented as a cylinder and communicating with the mold cavity (KV) in such a way that the repository space (A) discharges without transition into the mold cavity (KV), whose volume nearly corresponds with the volume of the mold cavity (KV), and the molding material is conveyed out of the repository space (A) into the mold cavity (KV) by means of a piston (S) which is axially displaceable in the repository space (A), characterized in that at the beginning of the injection process, the piston (S) is at a first dead center, at which the bottom of the piston aligns with the edge of the repository space (A) and with the wall of the mold cavity in such a way that a small amount of molding material melt reaches the mold cavity (KV) directly, the piston (S) then slides into the cylinder and the repository space (A), which becomes larger continuously, is filled with molding material melt at almost no pressure until the piston (S) reaches its second dead center position and the supply of the molding material melt is ended, the piston (S) is then moved almost to the first dead center position and the mold cavity (KV) is thus completely filled with molding material, and during the dwell time, the piston (S) is brought into the first dead center position. 2. Molding process according to Claim 1, characterized in that as the movement path of the piston (S) from the second dead center position to shortly before the first dead center position increases, its movement speed decreases. 3. Molding process according to Claim 1 or 2, characterized in that the maximum volume of the repository space (A) is slightly larger than the volume of the mold cavity (KV). 4. Molding process according to Claim 1, 2, or 3, characterized in that the molding material melt reaches the repository space (A) through a channel (K) running through the inside of the piston (S) and discharging in the bottom of the piston. 5. Dosing device for molding machines having a molding material preparation device and a mold cavity (KV), formed by means of a first and a second mold plate (PF1, PF2), which is filled up with molding material, with the outlet (E) of the molding material preparation device connected with an accommodation space (A) whose volume can be changed and whose largest volume corresponds to at least volume of the mold cavity (KV), the accommodation space (A) connected by means of the opening with the mold cavity (KV) and occurring in a bushing between the face of a plunger (S), which is translationally movable in the bushing to serve for displacement of the molding material out of the accommodation space (A) into the mold cavity (KV) and provided with a through channel (K) for filling of the accommodation space (A), and the mold cavity (KV) when the plunger (S) assumes a rear position, and the face of the plunger (S) is flush with the edge of the opening when the plunger (S) assumes a forward position, characterized in that the plunger (S) is rigidly mechanically connected with the molding material preparation device (E), the bushing implemented as a component of the first molding plate (PF1) has available a first opening into which the plunger (S) dips and. a second opening located opposite to the first opening and directly connected with the mold cavity (KV), and the plunger (S) is provided with a stop (M) which presses against the edge surrounding the first opening of the bushing in the forward position of the plunger (S). 6. Dosing device according to Claim 5, characterized in that the plunger (S) consists of thermally conducting material (WS) on at least its free end. 7. Dosing device according to Claim 5 or 6, characterized in that the plunger is provided with a heat exchanger (KS) which is connected into a cooling circuit. 8. Dosing device according to Claim 7, characterized in that the heat exchanger (KS) is thermally coupled with at least the face of the plunger (S). 9. Dosing device according to Claim 7 or 8, characterized in that the cooling circuit with the connected heat exchanger (KS) is implemented as adjustable. 10. Dosing device according to one of the Claims 5 to 9, characterized in that the second mold plate (PF2) consists of thermally conductive material (WF) in at least the region lying opposite to the second opening of the bushing. 11. Dosing device according to one of the Claims 5 to 10, characterized in that the second mold plate (PF2) is provided with a heat exchanger (KF) connected into a cooling circuit. 12. Dosing device according to Claim 11, characterized in that the heat exchanger (KF) is thermally coupled with the region of the second mold plate (PF2) consisting of thermally conductive material (WF). 13. Dosing device according to Claim 11 or 12, characterized in that the cooling circuit with the connected heat exchanger (KF) is implemented as adjustable. 14. Dosing device according to one of the Claims 5 to 13, characterized in that a union nut with a shank, which is screwed on to the outlet (ED) of the molding material preparation device (A), serves as the stop (M) of the plunger (S). 15. Dosing device according to one of the Claims 5 to 14, characterized in that the second opening of the bushing is closed mechanically when the plunger (S) assumes the rear end position. 16. Dosing device according to one of the Claims 5 to 15, characterized in that a number of bushings and an equal number of plungers (S) are provided, the plungers (S) are attached to a hot runner girder (B), the hot runner girder (B) is connected with the molding material preparation device, the hot runner girder (B) has at least one hot runner (H) into which the outlet (ED) of the molding material preparation device discharges, the channels (K) of the plungers (S) are connected with the hot runner (KH), and the hot runner girder (B) forms the stop for ending of the relative motion between the plungers (S) and the bushings. 17. Dosing device according to Claim 16, characterized in that a hot runner (KH) is provided with a number of outlets, which discharge into the plunger channels (K), corresponding to the number of plungers (S) and bushings. 18. Dosing device according to Claim 16, characterized in that a number of hot runners (KH), positioned in a star shape, which corresponds to the number of the plungers (S) and bushings, connect the discharge of the outlet (ED) of the molding material preparation device with the plunger channels (K). 19. Dosing device according to Claim 16, 17, or 18, characterized in that the hot runner girder (B) is provided with a heating device (HK). 20. Dosing device according to Claim 19, characterized in that the heating device (HK) is adjustable.